How to improve the light extraction efficiency is always an important issue in the development of light-emitting diode. One reason that the light extraction efficiency is difficult to improve is that internal reflections or refractions from the light-emitting diode chip itself and interfaces between the light-emitting diode chip and peripheral devices cause the light emitted from the light-emitting diode chip to be absorbed by the peripheral devices. In order to solve this problem, the light-emitting diode is typically covered with a titanium dioxide-containing housing. Titanium dioxide can improve the reflectivity to visible light. Such a housing is typically made of polyphenylhydrazine (PPA) engineering plastics. However, the drawback of such an approach is that the use of titanium dioxide will cause the PPA housing to gradually become yellowish, and hence the light extraction efficiency is reduced.
Another conventional approach is disclosed in US 2010/0032702, which uses fluoro-containing engineering plastics instead of PPA. In such an approach, the housing is made of fluoropolymer by injection molding to solve the yellowish problem. However, since the fluoropolymer is much more expensive, the manufacturing cost for the housing significantly increases, resulting in difficulties to practice on various light-emitting diode devices.